Add option for timed /sync cache

[ShadowJonathan]

This adds the experimental_features.sync_cache_timeout_ms config value. Thus this fixes #3880.

Stabilisation for general recommended use is left for a future PR or decision, after this has been tested enough (in my opinion).

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
• Pull request includes a sign off
• Code style is correct (run the linters)

Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>

[ShadowJonathan]

Folded into #9739